web3Enable(dappName: string): Promise<InjectedExtension[]> - to be called before anything else, retrieves the list of all injected extensions/providers
web3Accounts(): Promise<InjectedAccountWithMeta[]> - returns a list of all the injected accounts, accross all extensions (source in meta)
web3AccountsSubscribe(cb: (accounts: InjectedAccountWithMeta[]) => any): Promise<Unsubcall> - subscribes to the accounts accross all extensions, returning a full list as changes are made
web3FromAddress(address: string): Promise<InjectedExtension> - Retrieves a provider for a specific address
web3FromSource(name: string): Promise<InjectedExtension> - Retrieves a provider identified by the name
isWeb3Injected: boolean - boolean to indicate if injectedWeb3 was found on the page
web3EnablePromise: Promise<InjectedExtension[]> | null - null or the promise as a result of the last call to web3Enable

Usage

import { web3Accounts, web3Enable, web3FromAddress, web3ListRpcProviders, web3UseRpcProvider } from '@polkadot/extension-dapp';

// returns an array of all the injected sources
// (this needs to be called first, before other requests)
const allInjected = await web3Enable('my cool dapp');

// returns an array of { address, meta: { name, source } }
// meta.source contains the name of the extension that provides this account
const allAccounts = await web3Accounts();

// finds an injector for an address
const injector = await web3FromAddress('5DTestUPts3kjeXSTMyerHihn1uwMfLj8vU8sqF7qYrFabHE');

// sets the signer for the address on the @polkadot/api. The alternative approach it to pass the signer through
// options to signAndSend in the next step where we are sending (and skip this injection here), e.g
// `.signAndSend(<address>, { signer: injector.signer }, (status) => { ... })` 
api.setSigner(injector.signer);

// sign and send our transaction - notice here that the address of the account (as retrieved injected)
// is passed through as the param to the `signAndSend`, the API then calls the extension to present
// to the user and get it signed. Once complete, the api sends the tx + signature via the normal process
api.tx.balances
  .transfer('5C5555yEXUcmEJ5kkcCMvdZjUo7NGJiQJMS7vZXEeoMhj3VQ', 123456)
  .signAndSend('5DTestUPts3kjeXSTMyerHihn1uwMfLj8vU8sqF7qYrFabHE', (status) => { ... });